Comedy is hard, musical comedy e🍌ven harder, but Rob Reiner's fake "rockume✨ntary" about the US reunion tour of British heavy-metal gurus Spinal Tap manages to be both consistently funny and - particularly to the many genuine bands who have claimed it as a tour bus favourite - painfully plausible.

Reiner is dog-food ad director Marti DiBergi, whose mission is to capture "the sights, sounds and smells" of a rock band on tour. Sadly, the band in question is a hoary old bunch of has-beens with egos far in excess of their status. On vocals, David St Hubbins (Michael McKean), a self-con♉fessed "full-time dreamer" given to flights of laughably pretentious fantasy on the subtexts of songs such as Big Bottom and Sex Farm. On lead guitar, Nigel Tufnel (Christopher Guest), a bovine man-child in spandex, with a collection of literally untouchable six, 12 and, probably, 13-stringers. On bass, Derek Smalls (Harry Shearer), an impossibly ordinary, pipe-puffing lothario prone to unhelpful asides. A key running gag is the revolving-door policy regarding the other members, particularly an endless series of luckless drummers ("He died... In a bizarre gardening accident.")

Guest, McKean and Shearer had already gone beyond the call of duty - playing all the instruments and writing the songs - but Reiner lifts the film from standard satire to high comedy by nailing ܫeven more authenticity. He gives the band a history, mocking up lurid old flower-power showreels of the fresher-faced, `60s Tap, and inviting them to reassess their early albums ("Shark Sandwich was 🍨just a two-word review... `Shit Sandwich'). Along the way, we meet their bolshie manager Ian Faith (Tony Hendra), surly drivers, and, of course, a startled set-designer whose Stonehenge model is far from adequate.

The cine re-r🅺elease should be a welcome break for all those worn-down videos, and, inevitably, it'll place the glorious grandiosity of The Tap into a whole new perspective. Too much fucking perspective..꧑.